1. Field of the Invention
The present invention relates to a substrate provided with a bank and a substrate provided with a color pattern such as a color filter for use in a display device such as a liquid crystal display device.
2. Description of the Related Art
A color filter that is used for color separation in color liquid crystal display devices or image pick-up elements comprises colored pixels of a plurality of colors (for example, red (R), green (G), and blue (B)) and a light shielding bank (black matrix) that partitions the colored pixels. Such color filters have been often produced by a method based on photolithography using a photosensitive resin composition having a pigment dispersed therein as a coloration material. Such a method will be described below with reference to a typical color filter comprising a black matrix and RGB pixels.
First, a black matrix is formed on a substrate. The black matrix can be formed of a light shielding material that does not transmit visible light, and a metal material such as chromium or an inorganic material can be used therefor, but in recent years, resin black matrixes having light shielding particles dispersed in a photosensitive resin have often been used. In this manufacturing method, a light shielding photosensitive resin composition (black resist) is coated on a substrate such as glass, exposure is performed via a mask having the black matrix pattern, development is carried out with a liquid developer such as an alkali, and finally post-baking is performed, for example, at a temperature of 230° C.
A red photosensitive resin composition (color resist) is coated to a predetermined film thickness on the substrate that have thus been provided with the resin black matrix, exposure is performed via a mask of red pixel pattern, and alkali exposure and post-baking are then performed in the same manner as in the formation of the resin black matrix, thereby forming red pixels. Green pixels and blue pixels are then formed in the same manner, and a color filter comprising the resin black matrix and colored pixels of a plurality of colors can thus be obtained. However, such a process for producing a color filter involves a very large number of steps.
Problems encountered in the manufacture of a resin black matrix substrate include the appearance of gas bubbles during color resist coating that are caused by defects of cross-sectional shape of the black matrix, peeling of a black matrix resist film during alkali development, and appearance of residue. Furthermore, problems encountered when a color resist is patterned include misalignment of pixels of a plurality of colors, overhanging of cross-sectional shape of pixels, appearance of pixel defects or color retention caused by inadequate conduction of an ITO film, and appearance of residue.
Yet another problem that is often encountered is mask contamination that is caused by adhesion of color resist sublimates to the mask during exposure. In the photolithographic method, production yield of each step is not sufficiently high. Therefore, the production yield of the entire process is poor, thereby increasing the production cost of color filters.
A high production cost of color filters is due not only to a poor yield, but also to a high cost of glass substrates and black and color (red, green, blue) resist materials. The development of inexpensive color filters is needed for customers such as panel makers and in the industrial field of color filters, and at present, production methods based on printing process and ink-jet process are intensively studied.
With the ink jet process, ink is selectively ejected on a specific region of a target from ultrafine ink nozzles, and specific sections of the object are colored. Ink-jet processes used for manufacturing a color filter can be generally classified into those in which ink receptacles are provided on a color filter substrate that is a target and the ink is fixed, and those in which fine partitions are provided to prevent ink from overflowing. In the latter case, a black matrix provided on the substrate serves as the partitions. A color filter is thus manufactured by ejecting and charging an ink comprising a pigment of a necessary color into a specific region partitioned by the black matrix and then curing the ink to form a colored pixel.
With photolithography, a color resist has to be coated on the entire substrate surface. Therefore, a large amount of resist is wasted. Moreover, coating, exposure, development and post-baking steps have to be repeated as many times as there are colors. By contrast, with the ink-jet method, ink is not wasted, and although a large number of nozzles have to be provided, a plurality of colors can be charged at the same time and the curing process also can be completed in one step.
When a color filter is manufactured by the ink-jet process, color inks of a plurality of colors have to be printed without mixing. Pixels are partitioned by a black matrix, but the problem is that the printed inks overflow the partition walls of the black matrix and are mixed.
Patent Documents 1 and 2 disclose ink-repellent black matrixes. These documents describe inventions in which surface energy of a black matrix is decreased by a fluorine-containing or silicone compound, whereby printed inks of a plurality of colors are prevented from overflowing the black matrix and mixing, wherein ink repellency is imparted by admixing a compound or fine powder particles of the fluorine-containing or silicone compound to a carbon black ink or laminating on the upper surface of black matrix.
When fine powder particles of a fluorine-containing or silicone polymer compound are admixed, because the height of black matrix is typically within a range of 1-3 μm, the particle size has to be at least 0.2 μm or less for uniform ink repellency to be demonstrated, and such fine powder particles of polymer compounds are an extremely expensive material that increases the production cost. Furthermore, such ultrafine polymer particles are easily aggregated and a homogeneous dispersion is difficult to obtain. For these reasons, it can be said that the research using ultrafine polymer particles is difficult from the standpoints of both cost and technology.
Further, with the method of adding a fluorine-containing or silicone compound having a low molecular weight, ink repellency of black matrix is increased, but the addition of a fluorine-containing or silicone compound having a low molecular weight typically causes bleeding or blooming due to poor mutual solubility with the resin, the compound adheres to the printing locations of pixels, repels colored inks, and generates voids in pixels or causes adhesion defects of an overcoat layer.
Further, such compounds are dissolved as impurities in liquid crystals after a liquid crystal panel is assembled and cause display unevenness. Sufficient ink repellency is not demonstrated unless such materials with a low-surface energy are added in an amount of several percents. The increase in amount of the additives raises ink repellency, but causes problems associated with voids in pixels and adhesion, such compounds with a low surface energy have to be cleaned and removed, the number of production steps increases, and cost rises.    [Patent Document 1] Japanese Patent No. 3470352    [Patent Document 2] Japanese Patent No. 3430564